The present invention relates to a chip antenna for use, as an included antenna, and the like, in a portable telephone or a mobile terminal which is a wireless communication device, and a chip antenna unit in which the chip antenna is mounted in a mounting substrate.
Conventionally, a compact chip antenna for diversity reception, which is capable of being used in a plurality of frequency bands, such as 800 MHz band and 1500 MHz band, has been used in a mobile terminal, such as a portable telephone, or the like. An example of such a compact chip antenna is exemplified in, for example, Japanese laid open Official Gazette No. Hei 11-31913, namely, No. 1999/31913. In the Official Gazette, disclosed is a technique that the chip antenna has a conductor and a trap circuit inserted in an intermediate portion of the conductor and that two resonations, namely, a resonance by a whole of the chip antenna and another resonance by a portion of the conductor up to the trap circuit, are obtained.
Further, in Japanese laid open Official Gazette No. 2002/111344, disclosed is a technique that two resonances are obtained, respectively by a chip antenna and by a pattern antenna composed in a substrate.
As mentioned above, the two resonances can be obtained in the technique disclosed in the Official Gazette No. Hei 11-31913. However, not only a structure of the antenna becomes complicated but also antenna efficiency is deteriorated by resistance of the trap circuit.
Moreover, the antenna is fabricated on the substrate by a conductive path pattern in the technique disclosed in the Official Gazette No. 2002/111344. As a result, an antenna portion thereof becomes very large in size, in spite of requirement of fabricating the antenna in a smaller size.
Besides, what is called, a wide-band chip antenna is obtain d, when the respective resonant frequency bands of the two resonances in the chip antenna are rendered to be close to each other. Even if such a wide-band chip antenna is fabricated by the techniques disclosed in the above-mentioned Official Gazettes, problems similar to the above are inevitably caused to occur.
Under these circumstances, it is strongly desired to develop a chip antenna capable of obtaining resonances in a plurality of frequency bands or a broad frequency band in spite of a plain structure of the chip antenna.
In the interim, when a plurality of pattern antennas are located to be stacked on each other by making an antenna element have a stacked structure, a chip antenna having a plurality of resonances can be fabricated small in size with a plain structure thereof.
However, when frequency characteristics of one antenna are adjusted by altering a shape of the pattern antenna, frequency characteristics of the other antenna are also varied responsively. It therefore becomes difficult that the chip antenna is rendered to have an optimized resonant frequency.
On the other hand, when a chip antenna is mounted on a mounting substrate, it is sometimes caused to occur that frequency characteristics of the chip antenna are fairly varied under the influence of a path pattern, or the like.
In this case, since the frequency characteristics cannot be adjusted finely in the conventional chip antenna, the chip antenna itself must be replaced with another one Accordingly, it is necessary to prepare many kinds of antennas having frequency characteristics fairly different from each other, respectively. This makes productivity of the chip antenna units remarkably deteriorated.
Accordingly, it is an object of the present invention to provide a chip antenna capable of obtaining resonances in a plurality of frequency bands or a broad frequency band in spite of a plain structure of the chip antenna.
It is another object of the present invention to provide a chip antenna capable of rendering a predetermined pattern antenna to have an optimized resonant frequency without influencing frequency characteristics of the other pattern antenna.
It is yet another object of the present invention to provide a chip antenna capable of readily adjusting frequency characteristics thereof.